Unlock Memories Secret Level:
Enter the wooded area in the 'Flashback' level and search for the teddy bear. You will find it before your reach the building with the VHS tape player and television screen leaning against a tree near the edge of the cliff to your left. The secret 'Memories' level will start when you interact with the teddy bear.

Unlock Alternate Ending:
When you successfully complete the game on the Hardcore difficulty setting you will be able to view an alternate ending.

Easy 'Tangled' Achievement:
The area in the last chapter where the forest is on fire is the only place you can get this Achievement. When you reach this area stop moving and allow Slender Man to ensnare you with his tentacles.

Easy 'Master Pianist' Achievement:
In 'Part 1: Prologue' there is a piano in the house which if you use a few times will unlock the 'Master Pianist' Achievement.

Easy 'I Love Radio' Achievement:
In 'Part 1: Prologue' there is a radio inside the house which if you walk up to and use several times will unlock the 'I Love Radio' Achievement. You do not have to listen to the whole track for the Achievement to unlock.

Easy 'Fearless Fun' Achievement:
In 'Part 1: Prologue' go to the slide behind Kate's house and climb it's steps to reach the wooden fort. If you the use the slide you will get the 'Fearless Fun' Achievement.